Stomach tightening with mild cramps every 5 mins??? Is this

I am having regular stomach tightening with some mild cramping, I thought it might just be braxton hicks but they have continued for over the last hour about 5 mins apart or so (when I am sitting down resting) and will get stronger and closer together when I am up and walking. I really want to know if this is false labor or the real thing, my doc says my due date isnt till the 21st but from my calculations today would be my due date. Any advise?